Hey, I'm new at this too, so get confirmation before you take any recommendations from me!
I think others here would tell you it's all about the fuel. Lump charcoal will get your temp up quickly, then there's hardwoods (chunks or logs) such as mesquite, hickory, oak, maple.
Also, I've seen pics from guys using old blankets around the smoke box as insulators.
50's shouldn't be too much of a problem. I fire up the 'Dera in the 40's with mesquite chunks and am able to maintain 250-260*.
Did you make the mods listed in "Bandera 101"? Firebricks in the bottom on both sides, and a good charcoal basket (purchased mine from Spicewine) at a bare minimum. That'll solve many fire/temp control problems from the start.